1. Field of the Invention
The present invention relates to an image recorder and image recording method for correcting image distortion in continuous scanning systems such as spiral scanning systems to achieve high image quality.
2. Description of the Background Art
Some image recorders have employed continuous scanning systems such as spiral scanning systems to improve their recording speed. The spiral scanning systems are for performing a scan while continuously moving an image recording beam in a sub-scanning direction orthogonal to a main scanning direction relative to an image recording medium that is mounted on a recording drum (rotating drum) rotating in the main scanning direction, thereby to record an image along scanning lines inclined with respect to the main scanning direction.
In the spiral scanning systems, as shown in FIG. 19, the scanning lines are inclined at an angle xcex8c with respect to the main scanning direction X. A resultant image on the film has the shape of a parallelogram and is distorted.
The following is one of the techniques for correcting such image distortion.
This technique is for correcting image distortion by setting an angle difference between a write angle and a read angle to be equal to the angle of inclination of the scanning lines with respect to the main scanning direction. Here, the write angle is the angle at which image data is written into address space in a memory (buffer memory) for image data, and the read angle is the angle at which the image data is read out from the address space in the memory.
As shown in FIG. 20, this technique corrects image distortion by dividing an image into a plurality of blocks along the main scanning direction X and producing a shift in the sub-scanning direction Y in blocks for memory access to achieve the above angle difference.
Each of the blocks has Nc pixels (Nc=Nb/Na) arranged in the main scanning direction X, the value Nc being obtained by dividing the number of pixels Nb arranged in the main scanning direction X in a recording drum by the number of pixels Na that a recording head can record at a time in the sub-scanning direction Y (i.e., the width of one scanning line in the sub-scanning direction Y). Expressed differently, the surface area of the recording drum is divided into Na blocks along the main scanning direction X.
The blocks are then shifted in the sub-scanning direction Y by amounts determined for each block to achieve the above angle difference and in this condition, memory accesses are made to correct image distortion.
In this case, the xe2x80x9cshiftxe2x80x9d in the sub-scanning direction Y occurs at a discontinuous point between each block, and the number of xe2x80x9cshiftsxe2x80x9d to take place increases with increasing number of the blocks Na arranged in the main scanning direction X. Here, the amount of the xe2x80x9cshiftxe2x80x9d in the sub-scanning direction Y is one pixel in an image.
In the above conventional technique, if the number of pixels (frankly, the number of output channels) Na is small, the number of blocks is also small. Accordingly, the number of xe2x80x9cshiftsxe2x80x9d occurring in the main scanning direction X is small and relatively unobstructive.
However, as the number of pixels (output channels) Na increases, the number of blocks also increases, which increases the number of xe2x80x9cshiftsxe2x80x9d to take place each having a width of one pixel in the image. In such a case, the xe2x80x9cshiftsxe2x80x9d become perceptible to the human eye, causing a problem of image degradation.
Especially, with speedups in image recording, the number of output channels is increasing in recent years; for example, some image recorders have several hundreds of output channels. The fact is that the aforementioned problem becomes more evident.
In the above conventional technique, image distortion correction may be performed by improving a resolution (i.e., reducing the size of each pixel) in the sub-scanning direction Y to reduce the amount of xe2x80x9cshiftxe2x80x9d. This, however, brings another problem of increasing the required memory capacity. Besides, such an increase in memory capacity requires a higher processing speed of hardware and makes an increase in cost unavoidable.
A first aspect of the present invention is directed to an image recorder for recording an input image on an image recording medium along scanning lines inclined with respect to a main scanning direction, by using a continuous scanning system for performing a continuous scan in both the main scanning direction and a sub-scanning direction. The image recorder comprises: a recording head for outputting each pixel in the input image as a set of pixel units smaller than the pixel, the recording head having a higher resolution than the input image in the sub-scanning direction; a scanning section for performing a scan by continuously moving the recording head relative to the image recording medium in both the main scanning direction and the sub-scanning direction; a memory for storing image data of the input image; an access controller for, for access to the memory, setting an angle difference between a write angle and a read angle to be equal to an inclination angle of the scanning lines with respect to the main scanning direction, the write angle being an angle at which the image data is written into an address space in the memory, the read angle being an angle at which the image data is read out from the address space in the memory; and a shift controller for outputting image data read out from the address space in a position that is shifted in the sub-scanning direction by a shift amount responsive to the inclination angle, the smallest unit of the shift amount being the pixel unit.
The first aspect of the present invention can achieve more smooth, high-quality image distortion since image data read out from the address space in the memory is outputted in a position that is shifted in the sub-scanning direction by a shift amount responsive to the inclination angle, the smallest unit of which is the pixel unit. Further, the memory only needs to have the capacity responsive to the resolution of the input image, which minimizes an increase in the required memory capacity.
According to a second aspect of the present invention, in the image recorder, an image area of the recording head is greater in width than the scanning lines in the sub-scanning direction.
The second aspect of the present invention allows overlapping imaging and thereby can minimize detection of a gap between each scanning line.
According to a third aspect of the present invention, in the image recorder, the image area of the recording head has a width that is obtained by adding the width of the scanning lines and a width smaller than the width of one pixel in the input image.
The third aspect of the present invention allows overlapping imaging, thereby minimizing detection of a gap between each scanning line and reducing the required memory capacity with a minimum amount of overlap.
According to a fourth aspect of the present invention, in the image recorder, the memory substantially has a storage area corresponding to three main scans.
The fourth aspect of the present invention can thus reduce the required memory capacity.
According to a fifth aspect of the present invention, in the image recorder, an image area of the recording head has the same width as the scanning lines in the sub-scanning direction.
The fifth aspect of the present invention can thus perform imaging for each scanning line with a maximum use of the width of the image area of the recording head.
According to a sixth aspect of the present invention, in the image recorder, the memory substantially has a storage area corresponding to four main scans.
According to a seventh aspect of the present invention, in the image recorder, the recording head uses a spatial light modulator for recording an image on the image recording medium.
The seventh aspect of the present invention can thus achieve a high-resolution recording head.
According to an eighth aspect of the present invention, in the image recorder, the spatial light modulator is a diffraction grating light valve.
The eighth aspect of the present invention can thus achieve an especially high-resolution recording head.
According to a ninth aspect of the present invention, in the image recorder, a resolution ratio between the input image and the recording head is variable.
The ninth aspect of the present invention can thus vary the width of recording per one main scan according to the required image quality and can also select a combination of the recording speed and image quality.
The present invention is also directed to an image recording method.
Therefore, an object of the present invention is to provide an image recorder and image recording method for correcting image distortion in continuous scanning systems such as spiral scanning systems with a minimum increase in memory capacity, thereby to achieve high image quality.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.